Error opening .xlsx file


Three .xlsx files, less than 1Mb each. Data spreadsheets. Whenever I try to open them an error window appears with this message:
The file ‘other…xlsx’ is corrupt and therefore cannot be opened. LibreOffice can try to repair the file.

The corruption could be the result of document manipulation or of structural document damage due to data transmission.

Repairing them does not work.
Now, I have confirmed that those very files work with Microsoft Excel. The big problem I have is that I find myself unable to provide a log report or upload these files for review due to a Non Disclosure Agreement. The files are confidential.
The developer sent me an .xls version of the files and they seem to open without issues, besides some overlaping in the format.

What can I do for the .xlsx version of the files to work?

Thanks in advance

Addition info:

LibreOffice version: (x64)
Windows 7 64 bits

As a work-around, have you tried saving them to some different format in before opening them in LibreOffice, like csv?